The market for surface mounted Nonvolatile Real Time Clock (NRTC) devices, Nonvolatile Static RAM (NVSRAM) devices, and other lithium battery backed integrated circuits has been limited due to the physical characteristics of the battery and the crystal oscillator as well as the physical characteristics of the devices themselves.
Many current NRTC and NVSRAM devices consist of a large encapsulated part utilizing a package that must be installed by hand or wave soldering, or through the use of a special socket. However, because batteries and crystal oscillators are temperature sensitive, these devices cannot be surface mounted using reflow surface mounting techniques. Reflow surface mounting requires that the device be subjected to high temperatures (approximately 215.degree. C.) for proper attachment. These high temperatures damage the temperature sensitive batteries and crystals.
An additional problem with this technology occurs when the batteries of the devices are exhausted. When this occurs, the entire device must be removed and replaced with an new device. This creates higher costs to the user.
Because of these problems as well as the large size of the encapsulated parts, many electronic devices such as the laptop personal computer and other small scale computers have to be manufactured without these types of NRTC or NVSRAM packages.
Currently, the single chip surface mountable plastic leaded chip carrier (PLCC), small outline integrated circuit (SOIC), thin small outline package (TSOP), and small outline J-lead (SOJ) versions of the NRTC and NVSRAM are sold to electronic manufacturers without a battery or a crystal oscillator. It is the manufacturer who is required to mount a battery and a crystal oscillator on the printed circuit board after the device has been surface mounted.
A major problem with this configuration also occurs when a problem with the battery or the crystal oscillator arises or when the product has completed its useful life. When these situations occur the old battery and crystal oscillator have to be un-soldered prior to the installation of a replacement battery and crystal. This process is very timely and ultimately leads to higher manufacturing cost.
One device manufacture, SGS Thompson, has made a device having a battery and crystal module attachable to a modified NRTC device. The battery and crystal module has contact pins which extend from the module and are inserted into matching female receptacles in the NRTC device. The battery and crystal module is designed to be attached to the NRTC device after the NRTC device has been surface mounted.
While the SGS Thompson's device does have some advantages over the current DIP lead technology, the height of the device is still too large for many applications. In addition, because this device is a single chip device, the market demand for high density memory devices which combine a controller chip and a separator memory chip, can not be met.
Because of the female receptacles in the NRTC device, the NRTC device must be modified or custom made to accommodate the contact pins of the module. Therefore, these devices are not compatible with market standard NRTCs having TSOP, PLCC, SOIC, or SOJ chips.
An additional problem with the SGS device is that the cleaning materials used to clean surface mounted devices tend to get trapped in the female receptacles. Also, prior to the attachment of the battery and crystal module, the exposed contact pins of the module are highly susceptible to shorting during handling.
Currently, there also is a Low Profile Module (LPM) for NVSRAMs, which, like the SGS device, has some advantages over the DIP lead technology. However, the LPM requires the user to provide an additional socket which must be surface mounted prior to the installation of the LPM. Further, the socket and LPM device have a larger area and larger height associated with it due to the addition of the socket.